A variety of useful structures are made of various layers bonded to each other. One class of such useful structures includes a layer of polyurethane material among the other layers. For example, a layer of polyurethane may be bonded to a flexible substrate, either directly or with other layers in between. Such structures may be used, for example, in place of leather in footwear, upholstery, apparel, sports equipment, or other places where leather has been used in the past. When such structures are suitable as replacements for leather, they are sometimes called “synthetic leather.”
German Democratic Republic Patent Specification DD 237 191 describes polyurethane reactive systems involving a hydroxyl functional urethane prepolymer, an isocyanate functional urethane prepolymer, and an organotin catalyst. Organotin catalysts are sometimes undesirable because of their possible effects on safety and the environment. It is desired to make compositions that include at least one amine catalyst and that are suitable for making polyurethane-containing structures.